In recent years, the electronic equipment typified by, e.g., mobile phones or mobile information terminal equipment have been broadly spread, and for such equipment, size reduction, weight reduction, and a longer life have been strongly demanded. With this demand, batteries, particularly lightweight compact secondary batteries being able to have a high energy density, have been developed as power sources.
Such secondary batteries are not limited to the above-described electronic equipment, and it has been recently considered that the secondary batteries are applied to various applications typified by electric tools such as electric drills, electric vehicles such as electric cars, and power storage systems such as power servers for residential use. High-output high-capacity secondary batteries have been developed as the above-described power sources.
Patent Documents 1 to 3 as described below disclose the techniques relating to secondary batteries.